/* @keyframes gradientBG {
    0% {
        background-position: 0% 50%;
    }
    50% {
        background-position: 100% 50%;
    }
    100% {
        background-position: 0% 50%;
    }
}
#web_bg {
    background: linear-gradient(-45deg, #eb6100, #8fc31f, #8957a1, #e4007f);
    background-size: 400% 400%;
    animation: gradientBG 15s ease infinite;
} */
#web_bg {
    /* 背景图像的地址（url括号里）  */
    background: url(https://cdn.jsdelivr.net/gh/dada6969/images/images/1000442.jpg);
    /* 背景图像不重复 */
    background-repeat: no-repeat;
    /* 背景图像大小 */
    background-size: cover;
    /* opacity:0.2 */
  }